"NEW YORK -- Being a young tennis player just isn't what it used to be. In 1990, just a few months before Milos Raonic was born, Pete Sampras won the U.S. Open at 19 years old. It was the fourth time in a six-year span that a teenager had triumphed at a Grand Slam -- a 17-year-old Michael Chang won the 1989 French Open and Boris Becker, also 17, grabbed the Wimbledon title in 1985 and defended it in 1986.

In 2000, Raonic was just shy of 10 and already one of Sampras' biggest fans when his hero was overpowered by 20-year-old Marat Safin in the U.S. Open final. The following year, Sampras was beaten again by another 20-year-old, Lleyton Hewitt. In 2005, a 19-year-old Rafael Nadal won the first of his French Open titles.

Now, Raonic is 21 but still considered an up-and-comer rather than a contender at this year's U.S. Open. And it's not that the Canadian is lagging behind his peers -- he's actually the highest ranked out of all the latest touted prospects, a group that also includes Bernard Tomic, 19, Grigor Dimitrov, 21, and Ryan Harrison, 20.

The young guns like Bernard Tomic relish the thought of being the next Federer or Djokovic. But that dream will have to wait.

Reaching the second week would be considered an achievement for any of them. Any thoughts of actually winning it would be far-fetched. Raonic, the No. 16 seed, nearly found himself out in the first round before pulling through in five sets.

It wasn't like this when they first picked up a racket and began imagining themselves holding up trophies in the (not-too) distant future. But the road to the top is much longer now, and the dominance of Roger Federer, Nadal and Novak Djokovic means the younger generation has had to re-adjust its expectations.

"I loved growing up thinking that I could win a Grand Slam at 19, but little did I know that these guys came along and spoiled my fun," Tomic ruefully said this summer. "I think back 10 years ago, I mean, everyone could win a Grand Slam in the top 20."

Although those three have certainly reduced the opportunities for everyone else, there has also been a general aging of the ATP Tour during this period. Many more players are maintaining or even reaching their career bests in their late 20s or even past 30, once considered retirement age for a pro tennis player. And it's taking longer to break through. Tomic was the only teenager to make it directly into the main draw at the U.S. Open.

The trend can also be seen on the WTA Tour, where veterans abound the way wunderkinds once did and few players are making a Grand Slam impact before their early 20s.

There's a consensus about why this has happened.

"I think the game's just a lot more physical," said Harrison, echoing the words of John Isner, Andy Roddick and Andy Murray this week. "Because the courts used to be so fast and the balls were quick and everybody was playing a more aggressive game style, it wasn't as physically draining as it is now. So that's why it takes a little bit more time, because it's not just about being able to put together one win. To go deep into a tournament, you have to win match after match and your body has to hold up. And there's a lot of work that goes behind that. So it takes a little while."

"It's not as much about shot-making now as it is about kind of movement and that sort of thing," Roddick said.

That has meant young players have not just had to change the timetable of their ambitions, but in some cases also adapt their games.

"I served and volleyed all the time when I was a junior," said Harrison. "It's not something you can do exclusively anymore, because of the way the game is. And so making that adjustment was something I had to do whenever -- I was 12, 13, 14.

"The way points are constructed now is a little different from 10, 15 years ago."

So the watch for a changing of the guard goes on. Even the more established up-and-comers like Juan Martin del Potro, Marin Cilic, Ernests Gulbis and Kei Nishikori continue to be very much works in progress, with del Potro's 2009 U.S. Open victory remaining an isolated breakout.

For the most part, they haven't complained, preferring to work and wait.

"I haven't really thought about it too much," Raonic said. "I understand it's sport and stuff happens and you don't have control over too many things. You don't know when you're going to play well, when things are going to really come together for you."

It's just as well they're patient, because they might have to wait a while. But even if this generation hasn't been able to emulate the precocious champions they watched as kids, watching the way Federer, Nadal and Djokovic have climbed and stayed at the top means there's certainly no shortage of inspiration for them to draw on. "I think if I improve like the guys now in the top three, then I have a chance in the future," said Tomic.

With careers getting longer, that chance also might last a while. Young players may be older these days, but at least they still have plenty of time."